Multilayer SAW Resonator Electrodes for Size Reduction and Signal Quality
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Solution Overview
Problem
Acoustic wave devices, such as SAW resonators, face challenges in reducing size and suppressing spurious signals, with existing designs often being bulky and inefficient in signal propagation.
Innovation Solution
A multilayer piezoelectric substrate with interdigital transducer (IDT) electrodes comprising a higher conductivity upper layer and a denser lower layer, along with reflector electrodes, is used to reduce the size of SAW resonators by optimizing the thickness and material composition of the electrodes and dielectric layers, while maintaining acoustic wave propagation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional aluminum IDT electrodes are used, then electrical conductivity is high, but device size is large
Solution Approach 1:
The patent employs a composite electrode structure consisting of a tungsten lower layer and an aluminum upper layer. The tungsten provides high density (19.25 g/cm³) for compactness and acoustic wave control, while the aluminum layer maintains high electrical conductivity (3.5×10⁷ S/m) for efficient signal propagation. This composite material approach resolves the contradiction between device size reduction and signal propagation efficiency by combining materials with complementary properties.
Solution Approach 2:
The electrode structure applies local quality by assigning different materials to different layers based on their specific functions. The lower tungsten layer is optimized for acoustic wave interaction and device compactness, while the upper aluminum layer is optimized for electrical conductivity. This localized material optimization allows each layer to contribute its superior property, achieving both size reduction and maintained signal efficiency.
2Volume of moving object
If electrode thickness is reduced to shrink device size, then device compactness improves, but acoustic wave propagation efficiency deteriorates
Solution Approach 1:
The patent uses composite electrode materials with optimized thicknesses to maintain acoustic wave propagation efficiency while reducing overall device size. The tungsten layer thickness is set between 0.02λ-0.06λ and the aluminum layer between 0.03λ-0.07λ, where λ is the acoustic wavelength. The high density of tungsten compensates for reduced thickness, maintaining acoustic coupling efficiency, while the thin aluminum layer preserves electrical performance.
Solution Approach 2:
The patent optimizes the thickness parameters of each electrode layer relative to the acoustic wavelength λ. By expressing thickness as a fraction of λ and selecting specific ranges, the design maintains acoustic wave propagation efficiency even at reduced absolute dimensions. The parameter optimization ensures that the product of density and thickness remains sufficient for effective acoustic coupling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a 30% reduction in SAW resonator width and improved signal reflection, maintaining quality factor and coupling coefficient, thus enhancing the performance and compactness of acoustic wave devices.
Implementation Method 1
a layer of piezoelectric material having a lower surface bonded to an upper surface of a layer of a dielectric material
Implementation Method 2
the dielectric material having a lower surface bonded to an upper surface of a carrier substrate
Data Source
AI summary
A surface acoustic wave (SAW) resonator comprises a plurality of interdigital transducer (IDT) electrodes disposed on a multilayer piezoelectric substrate including a layer of piezoelectric material having a lower surface bonded to an upper surface of a layer of a dielectric material. The dielectric material has a lower surface bonded to an upper surface of a carrier substrate. The plurality of IDT electrodes include an upper layer and a lower layer. The upper layer is formed of a material having a higher conductivity than the lower layer. The lower layer is formed of a material having a higher density than the upper layer to provide for reduction in size of the SAW resonator.